In recent years, an individual identification technique utilizing radio communication such as radio waves or an electromagnetic waves has attracted attention. In particular, as a semiconductor device which communicates data by radio communication, an individual identification technique utilizing an RFID (Radio Frequency IDentification) tag has attracted attention. An RFID tag (hereinafter described simply as an RFID) is also referred as an IC (Integrated Circuit) tag, an IC chip, an RF tag, a wireless tag, or an electronic tag. The individual identification technique utilizing the RFID has been useful for production, management, and the like of an individual object and an application to personal authentication has been expected.
The RFID is divided into two types, depending on whether a battery is incorporated or power is supplied from outside one of which is an active-type RFID which incorporates a battery, and the other of which is a passive-type RFID which is driven by utilizing power of radio waves or electromagnetic waves (carrier waves) from outside (with respect to an active-type RFID, see Reference 1: Japanese Published Patent Application No. 2005-316724, and with respect to a passive-type RFID, see Reference 2: Japanese Published Patent Application No. 2006-503376). Between the two, in an active-type RFID, a power supply for driving the RFID is incorporated and a battery is included as the power supply. In addition, in a passive-type RFID, a power supply for driving the RFID is generated by utilizing power of radio waves or electromagnetic waves (carrier waves) from outside, so that a structure without a battery is realized.
FIG. 3 shows a block diagram showing a specific structure of an active-type RFID. In an active-type RFID 300 in FIG. 3, a communication signal received by an antenna circuit 301 is input into a demodulating circuit 306 and an amplifier 307 in a signal processing circuit 302. Usually, the communication signal is transmitted by applying processing such as an ASK modulation or a PSK modulation of a carrier such as 13.56 MHz or 915 MHz. Here, FIG. 3 shows an example in which 13.56 MHz is used as the communication signal. In order to process a signal, a clock signal which is a reference signal is needed in FIG. 3, and here, the carrier of 13.56 MHz is used as the clock signal. The amplifier 307 amplifies the carrier of 13.56 MHz and supplies it to a logic circuit 308 as the clock signal. In addition, the communication signal to which the ASK modulation or the PSK modulation has been applied is demodulated in the demodulating circuit 306. The signal after demodulation is also transmitted to the logic circuit 308 to be analyzed. The signal analyzed in the logic circuit 308 is transmitted to a memory control circuit 309, and based on it, the memory control circuit 309 controls a memory circuit 310 and takes data stored in the memory circuit 310 to send it to the logic circuit 305. The data stored in the memory circuit 310 is encoded in the logic circuit 305 and then it is amplified in the amplifier 304, and a modulation circuit 303 modulates the signal. Here, a power supply in FIG. 3 is supplied by a battery 321 through a power supply circuit 320. The power supply circuit 320 supplies power to the amplifier 307, the demodulating circuit 306, the logic circuit 308, the memory control circuit 309, the memory circuit 310, the logic circuit 305, the amplifier 304, the modulation circuit 303, and the like. The active-type RFID operates in this manner.
FIG. 2 shows a block diagram showing a specific structure of a passive-type RFID. In a passive-type RFID 200 in FIG. 2, a communication signal received by an antenna circuit 201 is input into a demodulating circuit 206 and an amplifier 207 in a signal processing circuit 202. Usually, the communication signal is transmitted by applying processing such as an ASK modulation or a PSK modulation of a carrier such as 13.56 MHz or 915 MHz. Here, FIG. 2 shows an example in which 13.56 MHz is used as the communication signal. In order to process a signal, a clock signal which is a reference signal is needed in FIG. 2, and here, the carrier of 13.56 MHz is used as the clock signal. The amplifier 207 amplifies the carrier of 13.56 MHz and supplies it to a logic circuit 208 as the clock signal. In addition, the communication signal to which the ASK modulation or the PSK modulation has been applied is demodulated in the demodulating circuit 206. The signal after demodulation is also transmitted to the logic circuit 208 to be analyzed. The signal analyzed in the logic circuit 208 is transmitted to a memory control circuit 209, and based on it, the memory control circuit 209 controls a memory circuit 210 and takes data stored in the memory circuit 210 to send it to the logic circuit 205. The data stored in the memory circuit 210 is encoded in the logic circuit 205 and then it is amplified in the amplifier 204, and a modulation circuit 203 modulates the signal. On the other hand, the communication signal input into a rectifying circuit 220 is rectified and input into a power supply circuit 221. The power supply circuit 221 supplies power to the amplifier 207, the demodulating circuit 206, the logic circuit 208, the memory control circuit 209, the memory circuit 210, the logic circuit 205, the amplifier 204, the modulation circuit 203, and the like. The passive-type RFID operates in this manner.